Intermittent fasting may be equally as effective for weight loss as counting calories

ARI SHAPIRO, HOST:

A standard piece of advice for those who want to lose weight is count calories. That can be time-consuming and hard to stick with. Well, a new study suggests you can get the same results with a simpler approach - intermittent fasting. NPR's Will Stone reports.

WILL STONE, BYLINE: One of the most common forms of intermittent fasting is to simply limit the amount of time you eat during the day, usually to about six to eight hours. Research has found this can help people lose weight over the course of a few months because they end up eating less. But Krista Varady says it wasn't clear just how well this worked over a longer stretch of time. Varady is a professor of nutrition at the University of Illinois, Chicago.

KRISTA VARADY: We really wanted to see, can people lose weight with this over a year? Can they maintain the weight loss?

STONE: So they recruited 90 adults with obesity from the Chicago area and then randomly assigned them to three groups. One could only eat between noon and 8 p.m. Another had to count calories and cut their daily intake by 25%. And the last didn't make any changes to their eating. At the end of the year, here's what the scales showed.

VARADY: You can basically achieve the same amount of energy restriction by just, yeah, counting time instead of counting calories. So both groups reduced their energy intake by about 400 calories per day.

STONE: And both groups lost on average about 5% of their body weight. Varady says the thing is, the fasting group wasn't told to cut down on calories. They did it on their own.

VARADY: We call it, like, an unintentional calorie restriction or, like, a natural calorie restriction that just happens.

STONE: She doesn't believe it was anything too complex. People just had less time to eat.

VARADY: People eat within, like, usually like a 12- to 14-hour window. So all we're doing is cutting out, like, you know, around six hours. Mainly we're cutting out, like, I think after-dinner snacks honestly.

STONE: She says they settled on noon to 8 p.m. because people generally like to eat later in the day when they fast. Dorothy Sears directs Clinical and Community Translational Science at Arizona State University. She says counting calories doesn't work for everyone trying to lose weight because you have to monitor everything you consume closely around-the-clock.

DOROTHY SEARS: It's difficult for people to do that, even me. Like, I got an app, you know, and I was frankly shocked at how many calories there were in a very small portion of nuts.

STONE: And life gets in the way. People go out to eat or grab a snack at a party and lose track. Sears says the take-home from this research is that time-restricted eating can be an easy alternative to counting calories.

SEARS: We don't have to arm wrestle which is the better one. But I think we do need to test whether it's effective. And think this study is showing, yeah, it's effective.

STONE: And people kept at it. Those who only ate between noon and 8 p.m. were able to do it about 90% of the time in the study. All of this is very encouraging to Courtney Peterson, who's a professor of nutrition at the University of Alabama at Birmingham.

COURTNEY PETERSON: It's not a fad diet in the sense of people can do it for three months, and they fall off the wagon for a year.

STONE: She says this is the first long-term comparison of time-restricted eating versus standard calorie counting. But it builds on a growing body of evidence, and she thinks it can help move the needle.

PETERSON: I think what we'll start to see is more and more dietitians offering intermittent fasting as an alternative to calorie counting. And you really need a long-term study like this to start developing those programs.

STONE: After all, she says, research suggests, and it makes sense, that many people would rather watch the clock than their calories. Will Stone, NPR News. Transcript provided by NPR, Copyright NPR.